In one fishing method calling trolling, a fishing line is pulled behind a slowly moving boat. Because the forward movement of the boat tends to cause the relatively light fishing line, lure and hook to rise in the water, a device called a downrigger is employed to maintain the hook and lure at the desired depth for the type of fish being sought. Downriggers generally consist of a relatively heavy weighted line to which the fishing line is coupled by a mechanism which releases the fishing line when the fish takes the baited hook.
Various types of downrigger release mechanisms have been employed. For example, in one type of device the fishing line is wrapped around a first element which is frictionally held by a second element secured to the downrigger line. The fishing line is released when sufficient force is applied to separate the elements. This type of release device is shown, for example, in U.S. Pat. Nos. 3,765,118; 4,069,611; and 4,177,599.
Another type of prior art release device holds the fishing line to the downrigger line by a spring biased retaining element. The fishing line is released when a fish exerts sufficient pull to overcome the retaining spring. Release elements of this type are shown, for example, in U.S. Pat. Nos. 2,858,637; 3,659,370; and 3,925,920.
Prior art release devices of the types discussed have not been entirely satisfactory because they tend to abrade or kink the fishing line. Another shortcoming of such devices is that the required release force cannot be readily adjusted for the requirements of different species of fish.
One attempt to overcome these shortcomings is disclosed in U.S. Pat. No. 4,031,652. This device employs an adjustable permanent magnet attached to the downrigger line and a magnetic member mounted on the fishing line. By adjusting the position of the permanent magnet, the degree of magnetic attraction between the magnet and the magnetic member can be controlled. While this device does permit some adjustment of the required release force, the magnetic member remains attached to the fishing line after release thereby creating a drag which might be sensed by some fish causing them to release the bait. Additionally, the removable release member could become lost if the line parts or if it slides off the end of the line.